1. Field of the Invention
The present invention relates generally to packaging semiconductor dies and more particularly to a method for packaging a semiconductor die containing one or more sensors and to a package resulting in particular from this method.
2. Description of Related Art
Without limiting the scope of the present invention, the background of the present invention is described in connection with the packaging of semiconductor dies containing one or more optical sensors, which can be any sensors designed to detect any spectrum of light, including infrared. Accordingly, the present invention is applicable to the packaging of any semiconductor die containing one or more sensors, such as fingerprint sensors, where conventional packaging techniques and materials reduce the effectiveness of the sensors.
Semiconductor dies or integrated circuits containing optical sensors, unlike most semiconductor dies, must be packaged in such a way as to allow light to contact the optical sensors and motion sensors, but still protect these sensors from environmental contamination. This is also true for infrared sensors, such as those used in integrated circuit fingerprint sensors. As a result, the performance and sensitivity of optical and other sensors can be significantly diminished by contaminants and moisture introduced during the packaging process, or by contaminants, air bubbles, irregularities and deformities in the packaging material itself.
In addition, some packages for semiconductor dies containing sensors utilize a transparent plastic resin or epoxy resin.
The use of a transparent plastic resin or epoxy resin, however, introduces additional problems. First, the most commonly used agents to facilitate the molding of the package and increase the package""s reliability cannot be used. Second, these transparent materials are harder to handle and clean out of the molds. Third, these materials are more expensive and require lengthy cure times (2 to 3 times that of a normal package).
Accordingly, there is a need for a method for packaging semiconductor dies containing one or more sensors that is durable, economical, efficient and effective. More specifically, the package should not significantly interfere with sensor performance while simultaneously protecting the sensors from foreign materials and contaminants.
The subject of the present invention is first of all a method for packaging a semiconductor die which comprises the steps of attaching a surface of a semiconductor die to a surface of a die carrier having external lead bonds or terminals, such that this die carrier does not extend in front of one or more sensors provided on the top surface of the semiconductor die and one or more bond pads on the top surface of the semiconductor die are coupled to one or more of the bond pads of said die carrier in an annular interface area formed between the top surface of the semiconductor die and a surface of said die carrier; encapsulating said interface area with a sealing ring; and encapsulating the bottom surface of the die carrier and a bottom surface of the semiconductor die with a packaging material.
According to an alternative embodiment of the invention, the method comprises the steps of: attaching a top surface of a semiconductor die to a bottom surface of a die carrier such that one or more sensors within the top surface of the semiconductor die are disposed below a first opening in the die carrier that is larger than the one or more sensors but smaller than the semiconductor die and an interface area is formed between said die and said die carrier where the top surface of the semiconductor die extends beyond the first opening in the die carrier and one or more bond pads on the top surface of the semiconductor die are coupled to one or more of the exterior terminals on the bottom surface of the die carrier; curing the semiconductor die attached to the die carrier; encapsulating the interface area with a sealing ring; curing the sealing ring; encapsulating the bottom surface of the die carrier and a bottom surface of the semiconductor die with a packaging material; and curing the packaging material.
According to the invention, the method may advantageously comprise the steps of: encapsulating an exterior portion of the interface area with a first sealing ring; curing the first sealing ring; encapsulating the bottom surface of the die carrier and a bottom surface of the semiconductor die with a packaging material; curing the packaging material; encapsulating an interior portion of the interface area with a second sealing ring; and curing the second sealing ring.
According to another alternative embodiment of the invention, the method comprises the steps of: attaching a bottom surface of a semiconductor die to a top surface of a recessed area of a pre-printed frame, the recessed area being larger than the semiconductor die, the semiconductor die having one or more bond pads on a top surface for providing terminals to one or more sensors within the top surface, and the pre-printed frame having one or more wire leads; curing the semiconductor die attached to the pre-printed frame; forming a dam to surround the recessed area to prevent a packaging material from entering the recessed area; curing the dam; forming wire bonds to couple each bond pad to a portion of one of the wire leads that is near the recessed area; encapsulating the wire bonds with a sealing ring; curing the sealing material; encapsulating the bottom surface of the pre-printed frame with the packaging material; and curing the packaging material.
According to the invention, the method may advantageously further comprise a step of applying a protective coating over the one or more sensors of the semiconductor die.
According to the invention, the method may advantageously furthermore comprise attaching a cap having a second opening larger than the sensors of the semiconductor die, the cap being attached to the top surface of the die carrier; and substantially encapsulating the cap with the packaging material.
Another subject of the invention is a semiconductor die package comprising a semiconductor die having one or more bond pads on a top surface for providing terminals to one or more sensors, in particular optical sensors, within the top surface; a die carrier which does not extend in front of said sensors and which has one or more bond pads comprising bond terminals and having external lead bonds, the bond pads of said die carrier and the bond pads of said die determining between them an annular interface area and being coupled in this area; a sealing ring encapsulating said interface area; and a packaging material encapsulating the bottom surface of the die carrier and a bottom surface of the semiconductor die.
According to the invention, the package may advantageously comprise a die carrier having a first opening larger than the one or more sensors but smaller than the semiconductor die and one or more external terminals; the top surface of the semiconductor die attached to the bottom surface of the die carrier such that the one or more sensors are disposed below the first opening and an interface area is formed where the top surface of the semiconductor die extends beyond the first opening in the die carrier and each bond pad is coupled to a portion of one of the external terminals that is exposed on the bottom surface of the die carrier; a sealing ring encapsulating the interface area; and a packaging material encapsulating the bottom surface of the die carrier and a bottom surface of the semiconductor die.
According to the invention, the sealing ring may advantageously comprise a first external sealing ring and a second internal sealing ring.
According to the invention, each bond pad is coupled to one of the external pads on the bottom surface of the die carrier by a solder bump.
According to the invention, the die carrier may advantageously comprise a substrate and each external terminal comprises a bond pad formed on a top surface of the substrate.
According to the invention, the die carrier may advantageously comprise a pre-printed frame and each external terminal comprises a wire lead.
According to the invention, the package may advantageously comprise a pre-printed frame having a recessed area which is larger than the semiconductor die and one or more wire leads, a bottom surface of the semiconductor die being attached to a top surface of the recessed area of the pre-printed frame; a wire bond coupling each bond pad to a portion of one of the external terminals near the recessed area; a dam surrounding the recessed area to prevent packaging material from entering the recessed area; a sealing material encapsulating each wire bond; and a package material encapsulating the bottom surface of the pre-printed frame.
According to the invention, the package may advantageously furthermore comprise a cap having a second opening similar in size to the first opening, the cap being attached to the top surface of the pre-printed wire frame and the packaging material substantially encapsulating said cap.
According to the invention, said sealing ring and/or said packaging material may advantageously comprise a thixotropic epoxy-based material.
According to the invention, the one or more sensors are covered with a protective layer.
According to the invention, the package may advantageously furthermore comprise a transparent encapsulation material in the first opening and on the top surface of the semiconductor die.
According to the invention, the package may advantageously furthermore comprise a lens disposed above the one or more sensors.